quantity packing

[millien]

I'm looking for something that adds multiple quantity of one product or create a pack of that product. 

a1 Product 1 = 1singel 

a2 produkt 1 = 10pack

a3 product 1 = 30 pack 

if the costumer wants to buy "a2"  the system should add 10 pieces of "a1" . and it should show in cart and checkout a2 , 1 quantity 

 

today we have always 10pack and in combination we remove the price , so it matches the singel price